Liquid chromatography (LC) is a technique for performing an analytical separation of a sample into constituent components, i.e., the analytes of interest to a researcher. As readily known by persons skilled in the art, during the course of a chromatographic separation, the sample is transported in a mobile phase (or solvent), which is a liquid in LC techniques. The mobile phase is forced through a stationary phase that is immiscible relative to the mobile phase. Typically, the stationary phase is provided in the form of a volume of particles (a column packing bed) supported in a column or cartridge through which the sample and mobile phase flow. The column packing bed is typically retained at each end of the column by a frit or filter that allows the mobile phase and sample to flow through while preventing the packing material from escaping the column. The frits are typically secured in place by end fittings located at the column inlet end and outlet end, respectively. The inlet end of the column is connected to an inlet conduit by which the sample/mobile phase is introduced into the column. A mobile phase reservoir, pump and sample injector are located upstream and interconnected to the column inlet via the inlet conduit. The outlet end of the column is connected via an outlet conduit to a suitable detector, which may operate based on ultraviolet or visible light absorbance, conductivity, fluorescence, light scattering, mass resolution, etc. In the column, the respective compositions of the mobile phase and stationary phase are selected to cause the analytes of the sample to become distributed between the mobile phase and stationary phase to varying degrees dependent on the nature of the respective analytes. Analytes that are strongly retained by the stationary phase travel slowly with the mobile phase, while analytes that are weakly retained by the stationary phase travel more rapidly. As a result, analytes of differing compositions become separated from each other as the mobile phase flows through the column. In this manner, the analytes are in effect sorted sequentially as the eluent flows out from the column, thereby facilitating their analysis by the detector.
The mechanical separation power or efficiency of a chromatography column depends in part on the physical attributes of the packing bed (stationary phase). To realize acceptable efficiency and resolution, the packing bed must be stable and uniformly packed. Dead spaces or voids within the packing material, or more generally reduced particle density, result in peak broadening and/or peak tailing observed in the acquired data and consequently loss of potentially valuable analytical information. Loss of stability or uniformity in the packing material may be caused by a number of factors, such as a poorly designed column packing process, a subsequent column assembly step that allows the density of the packing bed to be reduced, or subsequent use of the column in which the high-pressure fluid flow required for the LC technique destabilizes the packing bed.
The problem of providing a uniform, stable packing bed has been addressed in a few ways. In PCT App. Pub. No. WO 2004/024285, an LC column is taught in which a preformed filter assembly at the inlet end has a filter that includes a protruding portion. When the filter assembly is installed, the filter protrudes into the interior of the column where the packing bed is located to attain some compression of the packing bed. In UK Patent App. Pub. No. GB 2 429 939, an LC column is taught in which a metal filter is press-fitted into the open end of the column tube. Upon installation of an end fitting of the column, a metal compression body bears against the end of the tube of the column, which deforms the end of the tube. As the end of the tube yields in this manner, the compression body contacts the filter and causes the filter to bear against the packing bed to attain compression thereof.
In view of the foregoing, there is a need for providing chromatographic column hardware configured for improved longevity, mechanical stability and performance of the packing bed. There is also a need for providing a chromatographic column configured for uniformly compressing the packing bed contained in the column to a desired density level, and maintaining the uniformity of the density and stability of the packing bed during high-pressure chromatography operations.